The field of the invention extends in particular, but not exclusively, to the detection of leaks in small housings, for example housings for semiconductor components or watches.
From U.S. Pat. No. 4,608,866, a device for such application is known, wherein, during the insertion of the test objects, a test container is exposed to a purge gas atmosphere with approximately atmospheric pressure. After closing the test container, a valve is opened in the direction of a low temperature trap, so that the purge gas is evacuated before a valve is opened in the direction of a mass spectrometer and of a molecular pump arrangement associated therewith.
This device is complicated and expensive since it necessitates a very effective low temperature trap absorbing effectively all the purge carrier gas from the test container, so that no inadmissibly high total pressure can reach the mass spectrometer. The temperature of the low temperature trap is indicated with 16 to 22K.
If a primary pump were connected to the test container instead of the low temperature trap, so as to bring the container, after its closing, to a pressure convenient for the mass spectrometer prior to establishing the connection therewith, this would create the risk that already during this primary pumping phase, if the leak is large enough, also the inside of a test object would be evacuated to such an extent that lateron, i.e. during the actual measuring phase, no more helium atoms would be detected.
It is thus the aim of the invention to provide a simple device and a corresponding method of the kind indicated above, in which a high performance low temperature trap necessitating liquid helium or a refrigerator cryopump is not needed.